1. Field of the Invention
This invention relates to a method for developing a photoresist pattern, and more particularly to a method for developing a photoresist pattern wherein post-development defects are reduced.
2. Description of Related Art
Photolithography is an essential driver of the microelectronics industry. The ability to continually shrink designs to the point where sub-wavelength feature resolution is now routine, has allowed the industry to continue the trend toward higher device densities. To maintain this rate of development and to accomplish high device packing density, it has become necessary to incorporate sophisticated photolithographic processes.
Photolithography is the production of a three-dimensional image based on the patterned exposure to light and subsequent development of a light-sensitive photoresist on the wafer surface. Broadly stated, a radiation-sensitive photoresist is applied to a substrate such as a wafer and then an image exposure is transmitted to the photoresist, usually through a mask. Depending on the type of photoresist used, exposure will either increase or decrease the solubility of the exposed areas with a suitable solvent called a developer. A positive photoresist material will become more soluble in exposed regions whereas a negative photoresist will become less soluble in exposed regions. After exposure, regions of the substrate are dissolved by the developer and are no longer covered by the patterned photoresist film.
Unfortunately, as the demands of the microelectronics industry require smaller feature sizes, the line width defined by the resist is likewise becoming smaller. Yet, as the etch selectivity of resist to polysilicon or silicon nitride remains constant (or even decreases), the thickness of the resist also remains constant. This results in a higher aspect ratio of height to width of resist lines. With increasing aspect ratio, the mechanical stability of the resist lines decreases and post-development defects like resist collapses are likely to appear on the substrate.
Pattern collapses may have a dramatic impact on IC device yield. Hence, elimination of these defects becomes increasingly important in both research and development and manufacturing environments. Any delay in addressing the causes and cures of these yield killers can prolong the development cycle and production release of new product technologies. It is therefore crucial to develop new photolithographic processes that reduce the presence of post-development defects at critical mask layers.